Field of the Invention
The present invention relates to the field of bioelectricity. More particularly, the present invention provides energy generating systems, methods, and devices that are capable of converting chemical energy stored in a variety of renewable sugars into useful electricity. In specific embodiments, the present invention relates to novel synthetic enzymatic pathways for converting chemical energy from six-carbon and five-carbon sugars to electricity using enzymatic fuel cells, and several key enzymes with engineered and/or newly-discovered functions.
Discussion of Related Art
Batteries are electricity storage devices. Rechargeable batteries are currently available. But, the energy storage densities of such rechargeable batteries are much lower than those the energy storage densities of hydrogen or liquid fuels (FIG. 1, Panels A and B). There is a clear need for better rechargeable batteries (FIG. 1, Panel C) with higher energy storage density, lower costs over their entire life cycle, reduced environmental impact, and increased safety.
Enzymatic fuel cells (EFCs) are a type of biological fuel cells that employ enzymes to convert the chemical energy in the fuels into electricity. EFCs are superior to batteries mainly because they: 1) have approximately 10-100 times higher energy storage densities than chemical batteries; and 2) are more environmentally friendly due to the biodegradability and elimination of heavy metals and costly rare metals. EFCs (FIG. 2, Panel B) have some things in common with directed methanol fuel cells (DMFCs) (FIG. 2, Panel A). But, unlike DMFCs, the enzymatic fuel cells do not need costly platinum as an anode catalyst, and they may not use nafion membrane due to high selectivity of enzymes. In addition, sugars used in EFCs are less costly, non-toxic and, non-flammable compared to methanol in DMFCs, with energy densities of a sugar solution being higher than the energy densities of 1 M methanol solution. Enzymatic fuel cells are usually composed of an enzyme-loaded (enzyme-modified) anode and an enzyme-loaded (enzyme-modified) cathode (FIG. 2, Panel B).
In EFCs, electrons are generated when fuels are oxidized at an anode. The electrons then flow from the anode through an external load to a cathode. Protons are generated simultaneously (with the electrons) in the anodic reactions and pass through the polymer separator to the cathode to compensate for the electron flow. One of the largest challenges with EFCs is the extraction of most or all of the chemical energy from the low-cost and most abundant sugars for electricity generation. The methods to utilize the all energy of the sugars have not been developed so far, except for the methods that utilize sugars as a heat energy source by combustion in air or as a chemical energy source for the production of ATP through NAD(P)H generated by redox enzymes in living organisms (such as microorganisms, animals). There is no method that is capable of effectively utilizing most of the chemical energy of sugars directly as electric (electrical) energy.